Index: utils/TableGen/AsmMatcherEmitter.cpp
===================================================================
--- utils/TableGen/AsmMatcherEmitter.cpp
+++ utils/TableGen/AsmMatcherEmitter.cpp
@@ -310,11 +310,16 @@
     /// The suboperand index within SrcOpName, or -1 for the entire operand.
     int SubOpIdx;
 
+    /// Whether the token was a "new" token, i.e., it was preceded by a token
+    /// separator (for instance whitespace).
+    bool IsNewTok;
+
     /// Register record if this token is singleton register.
     Record *SingletonReg;
 
-    explicit AsmOperand(StringRef T)
-        : Token(T), Class(nullptr), SubOpIdx(-1), SingletonReg(nullptr) {}
+    explicit AsmOperand(bool IsNewTok, StringRef T)
+        : Token(T), Class(nullptr), SubOpIdx(-1), IsNewTok(IsNewTok),
+          SingletonReg(nullptr) {}
   };
 
   /// ResOperand - This represents a single operand in the result instruction
@@ -805,7 +810,10 @@
 
 void MatchableInfo::addAsmOperand(size_t Start, size_t End) {
   StringRef String = AsmString;
-  AsmOperands.push_back(AsmOperand(String.slice(Start, End)));
+  bool IsNewTok =
+      !Start || (isspace(String[Start - 1]) || String[Start - 1] == ',' ||
+                 String[Start - 1] == '$');
+  AsmOperands.push_back(AsmOperand(IsNewTok, String.slice(Start, End)));
 }
 
 /// tokenizeAsmString - Tokenize a simplified assembly string.
@@ -960,6 +968,11 @@
                                       std::string &RegisterPrefix) {
   StringRef Tok = AsmOperands[OperandNo].Token;
 
+  // If wasn't separater from another token (e.g. with whitespace), don't
+  // interpret this as a register name.
+  if (!AsmOperands[OperandNo].IsNewTok)
+    return;
+
   if (RegisterPrefix.empty()) {
     std::string LoweredTok = Tok.lower();
     if (const CodeGenRegister *Reg = Info.Target.getRegisterByName(LoweredTok))
@@ -1508,7 +1521,7 @@
       // Insert remaining suboperands after AsmOpIdx in II->AsmOperands.
       StringRef Token = Op->Token; // save this in case Op gets moved
       for (unsigned SI = 1, SE = Operands[Idx].MINumOperands; SI != SE; ++SI) {
-        MatchableInfo::AsmOperand NewAsmOp(Token);
+        MatchableInfo::AsmOperand NewAsmOp(/*IsNewTok=*/true, Token);
         NewAsmOp.SubOpIdx = SI;
         II->AsmOperands.insert(II->AsmOperands.begin()+AsmOpIdx+SI, NewAsmOp);
       }